The DarkroomSetting The Black Point; A Key Step In Getting The Right Tonal Range

One of the secrets to making
great ink jet prints is to set the black point correctly in the image
file before sending the image to the printer. The black point in an
image is the group of pixels that should be printed as solid, D-max,
black. If this setting is made correctly, it will establish a correct
tonal range for the image, which means that there will be a correct
distribution of shadows and highlights. You will have the proper density
in the shadows to allow you to have a maximum of shadow detail as well
as a maximum of detail in the highlights. As with many procedures in
Photoshop, different experts have different opinions on just how to
set the black point. So, before you all start writing in to tell me
how wrong I am, let me say up-front that this is how I set the black
point in my images, and this is why I do it this way. You're free,
to experiment with better options.

Image #1 was taken at Baltimore's Inner Harbor on a cloudy, overcast
day. The original image file was a tad low in contrast and a bit dull.
After opening the image in Photoshop (I'm using Version 7.0, but
the technique I'm describing will also work with Version 5.5 as
well as CS), go to Layer to New Adjustment Layer to Curves. When the
New Layer window opens, click on OK. That will cause the Curves adjustment
window to open. Click on OK. We'll come back to this adjustment
layer in a few minutes.

#2

Next, go back to Layer to New
Adjustment Layer to Threshold. When the Threshold New Layer window opens,
click on OK. That will open the Threshold adjustment window and will immediately
turn the image into a high contrast, black and white view as shown in
#2. In the Threshold adjustment window notice the little arrowhead under
the histogram (#3). Grab the arrowhead and drag it all the way to the
left and the image will go to solid white. Then, slowly drag the arrowhead
back to the right until you get just the beginning trace of some black
pixels (#4).

Use the CTRL plus the "+" key to magnify the image. Adjust
the scroll bars as you magnify the image until the group of black pixels
are in the middle of the window and large enough to see them clearly.
Place your cursor (an eyedropper) in the middle of the group of black
pixels, hold down the Shift key, and left click. A small circle with the
number one will appear (#5). Now click on Cancel.

#3

Next, go to the Layer Palette
(#6) and double click on the first square for the Curves adjustment layer
that we created earlier (see the red arrow in #6). That will cause the
Curves adjustment window to open (#7).

Back in #5 when you set the Threshold point, Photoshop also adjusted the
red, green, and blue curves to make the Threshold point absolutely neutral
in color balance. You can see the adjustments that Photoshop made by going
to the Channel dialog box and selecting the color channels one at a time
and looking at how they are now set. In #7, you can see that the Green
channel has been offset from the corner to the right just a little (see
the red arrow in #7).

#4

At this point, some experts
will tell you that you have correctly set the black point. I disagree.

If you will open the Info Palette and look at the RGB values (#8), you'll
see that the black point that has been set is now reading "0"
for all RGB values. Notice that before I made the black point adjustment
for this image the red value had been 12, the green value had been 16,
and the blue value had been 20 (#8). Since all three color channels have
now been set to "0," the shadows have had their color balance
set to neutral. If your printer is correctly calibrated, your shadows
will now print neutral black/gray with no trace of a color tint. This
can be especially valuable if you are printing pictures of men in black
tuxedos (like at a wedding). How often have you seen black tuxedos with
a blue or green cast in them?

#5

Here's where I differ
with some of the experts on setting the black point by this method. If
you set a D-max area to RGB "0" (as we have done earlier),
the ink jet printer will lay down considerably more ink than necessary
to establish D-max. This means that slightly lighter shadow tonal areas
will also be getting a whole lot more ink than is necessary, causing some
of them to also go to D-max when they should have printed a little lighter,
thus producing more visible detail in the shadows. The way to prevent
this excessive ink lay down, and to get much better shadow detail, is
to set the black point to something between 10 and 13 instead of "0."
Here's how I do that:

#6

In #9, you see the Curves adjustment
window as it first opens when you double click on the Curves layer back
in #6. If you will go down to the bottom left corner of the Curves adjustment
window and grab the end of the diagonal line, then drag it up just a little
(#9), you will lighten the black point. In fact, if you will keep your
eye on the Info Palette window (#8) while you are dragging the diagonal
line up, you will see the values of RGB changing from "0"
to the desired 10-13 units that I mentioned earlier. In this example,
I have set the black point to 12 units. The 12 units show up in the Curves
adjustment window down at the bottom as "Output" = 12 (#9).

The last fine tuning, which
you might want to do, is also done in the Curves adjustment window. Drag
the window off to one side so you can see the bulk of your image and then
bend the curve into a very gentle "S" shape. This will produce
a slight increase in contrast in the image, and should be done according
to your personal artistic taste. There is no real right or wrong. Image
#10 shows my finished image. As you can appreciate, the subtle shadow
details will not reproduce very accurately in the magazine, but I can
assure you that the subtle shadow detail can be clearly seen in a real
ink jet print. For more information visit my website at: www.colorbat.com.